In lighting systems, full brightness, or light output, of the lamps used in the lighting system is not always needed or desired. For example, when sunlight is present in the area served by the lighting system, full brightness of the lamps may provide excessive lighting for the area or may exceed optimum lighting levels. It would be advantageous to have natural sunlight and artificial lighting from fluorescent lamps augment each other by dimming the artificial lighting to achieve a desired level of combined light intensity for the area. In other cases, there may be areas that do not require full brightness of lamps continually because there is not a need for the maximum level of light intensity all of the time. In addition, reduction in the light output of lamps generally results in a reduction in electric power consumed for lighting. This is a cost savings for the user.
Full range dimming of fluorescent lamps has been difficult to accomplish because a minimum voltage must be maintained across the lamps to adequately charge gases within the lamp to produce light. Incandescent lamps are generally dimmed by reducing voltage across the lamps. If the voltage across a fluorescent lamp is reduced too greatly there will not be sufficient voltage to operate the lamp. Thus, dimming cannot be accomplished in the same manner as is done with incandescent lighting.
It can be appreciated that it would be advantageous to have a method and apparatus for dimming fluorescent lamps over a full range from 100% brightness to 0% brightness.